The present invention relates to a method for measuring the intensity of aircraft strobe lights, and in particular, to a method for measuring the intensity of anticollision lights to ensure that the lights are in compliance with standards propagated by the Federal Aviation Administration regarding minimum effective intensity.
In 1971, the Federal Aviation Administration propagated safety guidelines which require that certain airplanes and other aircraft have anticollision systems to prevent accidents. Part of the anticollision system requirements relate to the use of flashing lights to warn those on the ground and other aircraft of the plane's location. See FAA Airworthiness Standards, Anticollision Light System, .sctn.23.1401, 25.1401, 27.1401, and 29.1401. These anticollision lights are usually strobe lights or rotating beacons. For ease of reference, the lights will be referred to as strobe lights.
The regulations required that the airplanes have lights with a minimum effective intensity of 400 candles when measured within .+-.5 degrees of a horizontal plane. The effective intensity is figured by: ##EQU1## where: I.sub.e =effective intensity (candles).
I(t)=instantaneous intensity as a function of time.
t.sub.2 -t.sub.1 =flash time interval (seconds).
Until recently, however, the FAA has not enforced these regulations. The primary reason for the FAA's nonenforcement is that, until now, there has been no practical method for testing anticollision lights to ensure that the lights comply with the guidelines. Prior to the present invention, the lights had to be removed from the airplane and sent to a lab. The lights were placed in light-tight rooms and then illuminated to determine the candles produced. If the lights were below the minimum standards, they could be replaced. A finding that the lights were above the 400 candle minimum was of little long-term comfort, however, because Xenon strobe lights have a half life of just over two months. An example of the decline in effective intensity is provided in FIG. 1A. As can be seen from the graph, the effective intensity of a light can quickly pass from acceptable to substandard, thereby rendering the aircraft unsafe. This occurs because each time the Xenon in the flash tube of the strobe light is activated, a small amount of material (principally metal) collects on the flash tube wall. The continued build-up of the material interferes with light leaving the flash tube, and will ultimately prevent the flash from being seen unless the flash tube is serviced.
Prior to the present invention, the only solution to achieve complete compliance was to remove each strobe light off of an aircraft every month or two and have the lights analyzed in a lab. This required a significant amount of man hours and equipment to manually disassemble the light from the aircraft and replace it after testing. Not only did this present a significant out-of-pocket cost, but also resulted in even greater expense in view of aircraft down time. It is not surprising that the aircraft industry was reluctant to perform the regular maintenance necessary to insure compliance with these safety standards.
Because of these problems, most airlines, as well as the FAA, have virtually ignored the regulations. In February of 1992, a worldwide FAA study found that no airline company was actually testing its strobes to ensure that they complied with the regulations. In fact, many airlines waited until the strobe lights were noticeably deficient to the naked eye before replacing the strobe light. Some even waited until the strobe lights stopped blinking altogether before replacing the flash tube. Because the naked eye, especially when close to the aircraft, is a poor judge of the effective intensity, merely looking at the strobe lights is an ineffective way of determining whether they comply with the FAA regulations.
There have been several aircraft accidents recently which could have been avoided had the anticollision lights been within the standards set by the FAA. In light of this, the FAA has recently indicated that it would require airlines and other aircraft companies to develop and implement programs to test and maintain their anticollision lights in accordance with the regulations.
Because no practical system for testing the lights is currently on the market, there is a great need for a method for on site measuring of light intensity of strobe lights on aircraft. There is a special need for such a method which is mobile and can be used without requiring unnecessary down time for the aircraft, and for a method which accurately tests the lights without the need of a light-tight room.